I just had the same problem as described in this post
win 7 64 bit 4 mb ram X2 processor
Administrator, two user accounts, and guest
happened upon update
message was "unloading registry hives" in very top bar
but Spybot had crashed (I waited a couple of hours)
system was still ok for other tasks, system had not crashed
after reboot spybot updated and re-immunized ok
machine has latest spybot and also Spyware blaster, avast, comodo, sd helper, t-timer